1. Field of the Invention
The present invention relates to a method of strengthening tubular plastic material and more specifically for strengthening polypropylene hose which is used in automatic washers.
2. Description or the Prior Art
Deforming plastic materials to change some of the characteristics of those materials is shown by the prior art.
U.S. Pat. No. 2,528,528 discloses a method for forming a plastic wheel cover which includes extruding a rod-like plastic member and passing it warm through a helical tube to form a plastic member which is thereafter cut and welded to produce a circular member which is formed into a plate-like sheet.
U.S. Pat. No. 2,920,352 discloses that the drawing and stretching of thermal plastic organic polymers can make permanent changes in the molecular orientation and thereby increase the physical properties of the polymer.
U.S. Pat. No. 3,470,583 discloses the use of a pair of rollers placed at an angle to the direction of travel of thinning filaments to produce a false twisting in a spun filament.
U.S. Pat. No. 3,491,928 discloses passing an oriented film through spaced apart parallel plates wherein one of the plates is reciprocated at a frequency and amplitude sufficient to cause the advancing film to break into fibers.
U.S. Pat. No. 3,843,435 discloses a process for making continuous tubular hoses wherein the hose is rotated and pulled over an annulus to expand it and is passed through a curing zone after the deposition of a strengthening layer of randomly oriented fibers.